1. Field of the Invention
The present invention relates to a particle beam treatment system, and more particularly to a particle beam irradiation apparatus for treating an affected part by irradiating it with charged particle beams comprising proton ions, carbon ions, or the like, and a treatment planning unit using this particle beam irradiation apparatus, and a particle beam irradiation method.
2. Description of the Related Art
A treatment-method for treating a patient with cancer or the like by irradiating the affected part of the patient with charged particle beams such as proton beams is known. The treatment system used for this treatment includes a charged particle beam generating unit, beam transport system, and treatment room. The charged particle beam accelerated by the accelerator of the charged particle beam generating unit reaches the beam delivery apparatus in the treatment room through the beam transport system, and after being scanned by scanning electromagnets provided in the beam delivery apparatus, the charged particle beam is applied from a nozzle to the affected part of the patient. A treatment method using such a treatment system is known that includes the steps of: stopping the output of the charged particle beam from the beam delivery apparatus; and in a state where the output of the charged particle beam is stopped, controlling the scanning electromagnets to change the irradiation position (spot) of the charged particle beam (so-called “scanning”) and to start the output of the charged particle beam from the beam delivery apparatus after the aforementioned change (see, for example, European Patent Application No. 0779081A2 [FIG. 1 and the like]).
In the above-described conventional particle beam treatment system, in order to reduce to a minimum the exposure of normal tissue to radiation and perform a proper treatment with neither too much nor too little irradiation, the beam delivery apparatus has an irradiation dose monitor and/or beam position monitor for estimating the irradiation dose distribution, located at the downstream side of the electromagnets and immediately in front of a patient to be irradiated. In many cases, this monitor is of a type that accumulates charges ionized by the passage of beams in a capacitor, and that reads the voltage induced by the capacitor after spot irradiation. The capacity of this capacitor is determined so as to permit the amount of ionized charges by the spot subjected to a largest irradiation dose.
For the above-described capacitor, as the capacity decreases, the output voltage increases, thereby enhancing the resolution. Conversely, as the capacitor increases, the resolution decreases. Such being the situation, if the difference in irradiation dose between the spot subjected to the largest irradiation dose and that subjected to the smallest irradiation dose can be reduced, the capacity of the capacitor could be correspondingly reduced to enhance the resolution. This would effect the possibility of detecting more correctly an actual irradiation dose. However, the aforesaid conventional art does not particularly give consideration to the above-described reduction of the difference in irradiation dose, thus leaving room for improvement in the detection accuracy with respect to the actual irradiation dose.
Meanwhile, when performing irradiation to each spot, a target irradiation dose is set on a spot-by-spot basis. Once an integrated value of irradiation dose detected by the irradiation dose monitor has reached the target value, a beam stop command is outputted to the accelerator, and in response to it, the accelerator stops the output of a charged particle beam. With typical accelerator such as a slow cycling synchrotron or a cyclotron, even if the beam stop command is inputted as described above, strictly speaking, it is not impossible that some amount of response delay occurs rather than the output of the charged particle beam immediately stops. In such a case, even after the aforementioned target value was reached, the charged particle beam continues to be applied to the pertinent spot for the time period during the response delay time. This leaves room for improvement in the control accuracy with respect to the irradiation dose of the charged particle beam.
Since the irradiation dose monitor is a machine, it is difficult to perfectly eliminate the possibility that the irradiation dose monitor causes a malfunction or failure. Also, since the target irradiation dose for each spot is usually a value transmitted from a data base or a value calculated based on the transmitted value, it is not impossible that an improper value is inputted at the stage of the transmission or the calculation. However, the above-described conventional art does not particularly give consideration to such a monitor abnormality or an input error. This leaves room for improvement in the prevention of excessive irradiation of charged particle beams due to the aforementioned monitor abnormality or input error.
Furthermore, when performing irradiation to each spot, a target irradiation dose is set on a spot-by-spot basis. Once the integrated value of irradiation dose by the irradiation dose monitor has reached the target value, a beam stop command is outputted to the accelerator, and in response to it, the accelerator stops the output of the charged particle beam. Regarding such a beam stopping function, it is not impossible that equipment associated with this function causes a malfunction or failure, as well. However, the above-described conventional art does not particularly take a malfunction of such a beam stopping function into consideration. This leaves room for improvement in the prevention of excessive irradiation of charged particle beams due to the above-described malfunction or failure of the beam stopping function.
Accordingly, it is a first object of the present invention to provide a particle beam irradiation apparatus, treatment planning unit using this, and particle beam irradiation method that are capable of improving the detection accuracy with respect to an actual irradiation dose during treatment using charged particle beams.
It is a second object of the present invention to provide a particle beam irradiation apparatus and particle beam irradiation method that are capable of enhancing the control accuracy with respect to the irradiation dose of charged particle beams.
It is a third object of the present invention to provide a particle beam irradiation apparatus and particle beam irradiation method that are capable of reliably preventing the excessive irradiation of charged particle beams due to a monitor abnormality, input error, or the like.
It is a fourth object of the present invention to provide a particle beam irradiation apparatus and particle beam irradiation method that are capable of reliably preventing the excessive irradiation of charged particle beams due to a malfunction or the like of a beam stopping function.
It is a fifth object of the present invention to provide a particle beam irradiation apparatus and particle beam irradiation method that are capable of reducing the treatment time when performing irradiation of charged particle beams for each of a plurality of layer regions in a target.